Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive, rapidly fatal neoplasms for which new therapeutic approaches are desperately needed. MPNSTs occur in up to ten percent of patients with neurofibromatosis type 1 (NF1) and are highly resistant to standard chemotherapeutic agents. We have been investigating the cell death promoting activities of chloroquine (CQ), a lysosomotropic agent, for almost ten years and have found that CQ induces autophagic stress and caspase activation in a variety of normal and malignant neural cell types. We have hypothesized that CQ-induced death results from inhibition of pro- survival autophagic pathways and stimulation of both apoptotic and non-apoptotic death pathways. Importantly, CQ-induced cell death involves both p53-dependent and p53-independent pathways and given that human MPNSTs show p53 mutations or deletions in up to 75% of cases, p53-independent death pathways may be particularly critical for effective MPNST therapy. CQ has recently been reported to be a potent adjuvant to standard chemotherapeutic agents in several animal models of cancer and in the treatment of human glioblastoma multiforme (GBM) patients. Prophylactic CQ administration has also been reported to inhibit both lymphoma formation and atherosclerotic disease in transgenic mouse models of these conditions. We recently found that several CQ-related compounds, including quinacrine (QA) and mefloquine (MQ), have ten-fold greater potency than CQ in killing MPNST cells in vitro. Both QA and MQ have better nervous system penetration than CQ and have been used safely in humans as anti-malarial agents. We have also discovered a number of FDA approved quinolone antibiotics with lysosomotropic properties that show significant tumoricidal activity on MPNST cells in vitro. In this application, we focus on the molecular pathways by which CQ, QA, MQ and other tumoricidal lysosomotropic agents promote MPNST cell death and will critically test the therapeutic potential of these compounds using orthotopic transplantation of MPNST cell lines in nude mice and transgenic mouse models of MPNST tumorigenesis and progression. In aim one, we will test the hypothesis that CQ and other lysosomotropic agents induce MPNST cell death through both apoptotic and autophagic death pathways that are at least in part regulated by altered subcellular distribution and activity of cathepsins, Bax activation of the intrinsic apoptotic death pathway, and disrupted autophagy. Aim two will test the in vivo tumoricidal activity of CQ-related compounds and quinolone antibiotics and their utility as MPNST prophylactic agents in robust mouse models of MPNSTs. In total, these highly integrated studies of MPNSTs will extend our previous investigations of apoptotic and autophagic death pathways, yield new insights into the clinical utility of lysosomotropic therapies for MPNST treatment and prevention, and provide a solid foundation from which to propose future human studies of CQ-related compounds and quinolone antibiotics in NF1 and MPNST patients. PUBLIC HEALTH RELEVANCE: Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive neoplasms that arise in approximately 10% of patients with neurofibromatosis type 1 (NF1) as well as in a significant number of non-NF1 patients. We have found that a variety of lysosomotropic agents such as chloroquine, quinacrine and quinolone antibiotics have significant MPNST killing activity in vitro. This application aims to define their mechanism of tumoricidal action and to test these lysosomotropic compounds in mouse models of MPNSTs.